I was always curious about this. In the states we have:

  • Lumber - Comes most commonly in 2 inch (2x4,6,8,10,12,16) and 4 inch (4x4,4x6) varieties.
  • Plywood - Almost always 4x8 feet
  • Drywall/Plasterboard - Various 4 foot varieties (4x8,10,12) and sometimes 5 foot.

Walls are typically framed with studs 16 inches on center, rafters and joists usually the same, but sometimes 24 inches on center. Ceilings are usually 8 feet high, or 10 feet in lots of newer construction.

How does this work in the metric world?

7 Answers 7


In Canada, while officially we are metric, all the construction work I've been around is done almost entirely in imperial. Everything comes in the same dimensions, and is referred to in feet and inches. Framing is done 16 or 24" on center, standard ceilings are 8' high.

Part of this may just be a hold-over from years of everyone doing that way, and then passing that on as they teach younger tradespeople. In school, I grew up learning the metric system, with the most exposure to feet/inches while doing fractions in math class.

I think part of it has to do with convenience and standardization as well: a "1.22 x 2.44m plywood" is awkward to say, and changing the dimensions slightly to 1.25 x 2.5 m would be strange. 16" (0.406m) centers is about the right distance for drywall, and so if you had 1.25m sheets of drywall, your centers would have to be 0.416m (or 16.4") to work out.. that's awkward to deal with.

Personally, I use a tape measure that has both centimeters and feet/inches on it, and often use cm if I'm measuring any more accurately than 1/8". One thing imperial has going for it, is the foot is a very handy size. There is no equivalent in metric (the decimeter (10cm / 0.1m / 3.9") is too small (plus no one ever says the word "decimeter"), while the meter (3.28ft) is too big).

  • 1
    The dimensions stay the same so you can do work on old houses. I just extended an 80 year old drywall (plasterboard) wall, the studs needed to be the same dimension as what was there before - no problem. Commented Jul 24, 2010 at 6:19
  • 2
    @Jeremy: The problem with some old houses is that they used dimensional lumber. A 2x4 really was 2" by 4" rough cut so, in some cases, you have to use spacers to extend walls or do other similar work since a modern 2x4 has been milled to 1.5" by 3.5". Commented Jul 28, 2010 at 20:40
  • 1
    The main reason why Canadian dimensions are still imperial is that something like 75% of the lumber manufactured here goes to the US. Commented Jun 11, 2013 at 13:08
  • 1
    Canada is a metric company only in name. It's essentially imperial... with everything converted to metric. That's why we have 237 mL containers... and a 4.54 kg bag of potatoes. In any case imperial is an easier better system for wood construction, as you can much more easily deal with thirds and quarters so it's no surprise Imperial has stuck around. Don't @ me unless you know what a "Superior highly composite number" is in mathematics. Commented Jan 19, 2021 at 4:43

The following information is from Norway, but I would expect that the same dimensions are used elsewhere in Europe. The system used there parallels what we have here in the U.S., but the actual dimensions are different. Colloquially, terms like “two-by-four” are used, but the actual millimeter sizes are used in price lists, etc.

The dimensions referred to by the colloquial terms are quite a bit bigger than in the U.S. For instance, a U.S. milled four-by-four is actually 3.5 inches (89 mm). In contrast, a Norwegian milled “four-by-four” is actually 3.86 in (98 mm).

Here is a table I compiled with some common dimensions:

Milled structural lumber dimensions

Actual size (Europe) Actual size (U.S.) Nominal size (U.S.) 30 mm 1.18 in 36 mm 1.42 in 48 mm 1.89 in 38 mm 1.50 in 2 in 61 mm 2.40 in 73 mm 2.87 in 64 mm 2.50 in 3 in 98 mm 3.86 in 89 mm 3.50 in 4 in 123 mm 4.84 in 114 mm 4.50 in 5 in 148 mm 5.83 in 140 mm 5.50 in 6 in 173 mm 6.81 in 159 mm 6.25 in 7 in 198 mm 7.80 in 184 mm 7.25 in 8 in 223 mm 8.78 in

Unmilled lumber is sold in slightly larger dimensions: 100 mm, 125 mm, 150 mm, and so on.

Studs, joists, and rafters are always spaced 60 cm (23.62 in) on center. The dimensions of OBS and other sheets are multiples of 60 cm in both dimensions so they can be placed in either direction, e.g., 60 x 240, 60 x 300, or 120 x 300 cm.

  • 2
    That's smart to go with 60cm centers. One of the problem with metric is that it's based on decimal... and base 10 numbers get ugly when you divide them up. A 60cm base unit is even more flexible than a 12 inch foot! This is part of the reason why a 10' board is great. It's a 120" piece of wood. You can cleanly divide that into halves, thirds, quarters, fifths, sixths, eighths, tenths, and twelfths! Commented Aug 17, 2020 at 22:45
  • @Armstrongest messy is a weird way describe metric, but yes as long as nothing is smaller than an inch and you don't add or subtract anything less than a foot and nothing is divided by something not a prime factor of 12, imperial units can be handy.
    – sfscs
    Commented Jul 14, 2023 at 5:52

I'm from all metric country, but lot of stuff in constructing busyness are in "cols" that is inches. Again things like 2" or 4" are around 5cm and 10cm, so it's all round numbers.

  • just gotta comment, not about your answer, but about Slartibartfast! Nice reference! Commented Sep 22, 2022 at 12:26

Depends on the country. Most English-speaking countries use imperial system, but convert all the dimensions into m/cm/mm and kg. For example, this is a 2x4

However, it's usually not an issue outside of US/Canada, as most of the other world doesn't build houses out of dimensional lumber. They use bricks, cement blocks, cement panels, etc. and the dimensions are almost always communicated in millimeters

Most of the plumbing/windows-doors/etc. uses metric system.


(Un)fortuantely in Australia the dimensions are exactly the same. Which always throws me when I measure in MM and I go to the hardware store and they start talking in feet and inches.

It also answers questions about why some things are such incredibly odd dimensions. When you convert them from fractions-of-a-cm to feet/inches they usually fit some arcane measuring standard from the 1920s.

  • 1
    What's more, 2x4's aren't 2 inches by 4 inches, that's the measurement before they get planed. Commented Jul 24, 2010 at 1:26

Nobody uses fractions in the USA for small measurements, either.

Typical machinist measurements are in thousandths or ten thousandths of an inch. )

Engineers and surveyors often use feet and tenth of a foot.

Even carpenters don't always use standard fractional inches. A framing square has rules divided in 16ths, 8ths, 10ths, and 12ths. Use the most convenient.( a quality framing square also includes an inch divided in hundredths)

Brick masons course their brick in fractions of a foot. Their rules have divisions for 3,4,5, and 6 courses per foot.brick are sized so the brick and mortar joint come out even.

One of the beauties of feet and inches is there are lots of factors in the system, making it easy to divide something into equal parts, you can divide a foot into halves, thirds, quarters,sixths, and twelfths with no maths and whole units. Eights involves trivial math. With the inch using 16ths your odds of finding even divisions increases.

A meter or centimeter has only multiples of 2, 5 , and 10 as even factors.

The Elizabethans weren't stupid when they adopted the system. There is a reason the mile has 5280 feet in it. Try factoring it.

  • 4
    This doesn't answer the question.
    – Tester101
    Commented May 6, 2015 at 10:58
  • 1
    @Tester101 But it answers a bigger one. Not a believer in imperial, except for the fact that its more divisible, with useful chunks of distance, in the usable ranges.
    – dhaupin
    Commented Jan 19, 2017 at 4:18
  • Woodworkers, particularly cabinetmakers, use fractions extensively for small measurements down to about 1/128". Also... machinists very OFTEN use fractions. Commented May 11, 2023 at 14:49

The Canadian building industry is almost entirely homogenized with the US building industry. We use the same products so we use the same labels. Everyone here knows that a 2x4 isn't really 2"x4". 1/2" copper pipe was supposed to be 1/2" ID but the walls were too thin so instead of expanding the OD and making the connectors not fit, they made the ID small, so neither dimension is 1/2".

There are a lot of similar examples. The exception is plywood and gyproc which are really the given dimensions and thicknesses. There are a couple of differences between Canada and the US: Canadian shingles are 1m long, whereas the US shingle is 3 ft. long. Other differences are usually in measuring small thicknesses such as plastic and glass; normal household glass is 3mm. Its a lot easier using millimetres than fractions of inches for small values.

Not the answer you're looking for? Browse other questions tagged or ask your own question.